This invention relates to postage meters in which a print head utilized for printing postage indicia is removably mounted on the postage meter.
Postage meters include electronic means for carrying out accounting functions in respect of postage values which it is desired to apply to mail items by operation of a printer. The electronic means also carries out control functions for operation of the postage meter including operation of the printer. The accounting and control is carried out in a secure manner by housing the electronic means in a secure housing in order to protect the integrity of accounting data generated by the accounting means and to prevent fraudulent operation of the postage meter. It will be appreciated that it is also necessary, or at least desirable, to ensure that the printer cannot be operated to print postage indicia in respect of values for which proper accounting has not been effected. Accordingly the printer is usually housed, together with the electronic means, in the secure housing.
Previously postage meters have been provided with a drum printer or a thermal transfer printer for printing the postage indicia. With the drum printer, ink for printing the postage indicia is supplied by means of a replaceable absorbent roller containing liquid ink which rolls in contact with print dies on the print drum. With thermal transfer printers, ink is supplied as a layer on a replaceable ribbon which is fed past a thermal print head for transfer of ink to the mail items. Both the ink roller and the ink ribbon are removable from the postage meter by a user of the postage meter for replacement by a new ink roller or ink ribbon respectively. With both of these types of printer, the printer per se is maintained secure by the secure housing. In the case of the drum printer, mechanical elements for setting the printing elements of the printer are not accessible by a user of the postage meter and in the case of a thermal transfer printer, electrical connections to the print head for control and operation of the print head are protected from access thereto.
It is now proposed, instead of drum printers or thermal transfer printers, to use ink jet printing devices. Ink jet print heads are already used widely as computer output printers where security of operation thereof is neither a problem nor required. The ink jet print heads manufactured and sold for use in computer output printers comprise a module including a row of ink jet nozzles and means for ejecting selectively ink from those nozzles. The module also includes electronic circuits for operation of the ink ejection means and an ink supply to supply ink to the nozzles to replenish ink ejected from the nozzles in printing. When the ink in the ink supply is exhausted the entire module including the nozzles and electronic circuits is removed and replaced by a new ink jet print head module. It will be appreciated that the module is provided with electrical connections which, when the print head module is mounted in the postage meter, interface with similar connections of the postage meter.